Preparation of thermoset cycloolefin polymers via metathesis catalysts is a relatively recent development in the polymer art. Klosiewicz in U.S. Pat. Nos. 4,400,340 and 4,520,181 teaches a technique useful for preparation of such polymers from dicyclopentadiene and other similar cycloolefins via a two-stream reaction injection molding technique wherein a first stream, including the catalyst, and a second stream, including a catalyst activator, are combined in a mix head and immediately injected into a mold where, simultaneously, polymerization and molding to a permanently fixed shape take place.
In a system specifically taught by Klosiewicz, the ring-opening metathesis catalyst is based on tungsten hexachloride or tungsten oxytetrachloride. It is also known that the corresponding molybdenum compounds are effective ring-opening metathesis catalysts.
The tungsten or molybdenum catalyst is solubilized by complexing it with a phenolic compound so that a homogeneous catalyst/DCPD solution can be prepared. Also, in order to prevent premature ionic polymerization of the DCPD monomer in which the catalyst is to be dissolved, the catalyst component is stabilized by reacting it with a chelating agent or a Lewis base. Such chelants as acetylacetone, dibenzoyl methane, and alkylacetonates, or Lewis bases such as benzonitrile or tetrahydrofuran can be employed as the stabilizer. The chelants and, particularly, acetylacetone (2,4-pentanedione), are preferred stabilizers. Stabilization of the catalyst prevents ionic polymerization, giving the solution an almost indefinite shelf life in the absence of any activating mechanism taking place.
For a complete discussion of the preparation of such catalysts, reference can be made to Martin, U.S. Pat. No. 4,568,660.
Typically the stabilized catalyst is activated with an alkylating agent possessing a high degree of Lewis acidity to strip off the stabilizing ligand. The most frequently used activators for this purpose are the alkylaluminum or alkylaluminum halides. It is also known to use a mixture of trialkylaluminum and dialkylaluminum halide. A preferred system is a mixture of di-n-octylaluminum bromide and tri-n-octylaluminum.
While these catalyst systems work very well and have been employed in formulations which have been used in virtually all market penetration made to date by polymers of polycyclic cycloolefins, they sometimes present handling difficulties due to their high degree of sensitivity to air and moisture. This is particularly true of the alkylaluminum halide activators. These formulations must be protected from the atmosphere at all stages of handling, shipping, storage and use up to the time of charging into the mold.
This difficulty has been recognized and addressed in the art by Sjardijn et al, U.S. Pat. No. 4,729,976. Sjardijn discloses a catalyst system employing an unstabilized WCl.sub.6 /phenol complex, activated by a trialkyl or triphenyl tin hydride. As also disclosed by Sjardijn, this activator is quite insensitive to oxygen and moisture and, as a result, need not be handled in an inert atmosphere. However, this system is not suitable for use with stabilized catalyst complexes as it is not capable of removing the stabilizing ligand from the tungsten. Further studies have indicated that other known tin compounds behave similarly.